The present invention relates to a novel aromatic ester compound capable of exhibiting a second-order non-linear optical characteristic and a second-order non-linear optical material therewith.
It will be very essential in the coming highly information-predominant society in the near future to develop a highly efficient information-transmitting means by which a large amount of information of high precision can be transferred at a very high speed and in a high density. The optical technology is, along with the electronic technology in supplementation each to the other, expected to play a fundamentally important role in this technological field of information transmission by virtue of the unique and excellent characteristics of parallelism, space processability, adaptability to information processing of a large quantity and capability of high-density information transmission. In these days, several kinds of organic non-linear optical materials have come under highlight as a class of materials satisfying the requirements in the information transmission technology by optical means.
In contrast to the non-linear effect exhibited by the inorganic materials as reported heretofore, which is due to the absorption of lattice vibration, the non-linear effect exhibited by organic materials is due to the dipole moment produced as a result of the distortion in the .pi.-electron system by the substituent groups inherently without being accompanied by the lattice vibration enabling a high-speed response.
A second-order non-linear optical material is required to have high optical transparency and large non-linear optical characteristic. As a class of the second-order non-linear optical materials satisfying these requirements, attention is directed in recent years toward the so-called chained-chromophore organic non-linear optical materials. A chained-chromophore organic non-linear optical material here implied is an organic material developed under a concept that the value of .mu..beta., which is one of the characteristic parameters of second-order non-linear optical materials, is increased in proportion to the square of the number of units when non-linear active units are linearly combined together. Examples of known chained-chromophore organic non-linear optical materials include aromatic ester compounds and oligomers of an aromatic ester compound but these aromatic ester-based compounds, though having satisfactorily high transparency, are not very satisfactory in respect of the non-linear optical characteristics.
The second-order optical characteristic of a substance is a phenomenon which can be exhibited only when the substance lacks a center of symmetry. In polymeric materials, such a structure is obtained usually by the application of an electric field to the material to cause uniaxial orientation of the non-linear active species and a higher degree of the orientation results in greater performance of the material. One of the factors which greatly influence the degree of orientation is the dipole moment possessed by the molecules. The dipole moment of conventional aromatic ester compounds and oligomers of an aromatic ester compound, however, is not so large as compared with that of non-linear active species in general so that a high degree of orientation can hardly be obtained and, as a result, the second-order non-linear optical characteristic cannot be obtained or, even if it be obtained, cannot be high enough.